[Epoch Sync] How to ensure block headers are available for transaction validity period check?

[robin-near]

When a transaction is issued, it includes a block hash. The chain checks that the transaction's block hash is at most transaction_validity_period blocks old. This check requires BlockHeader to exist for the hash (not guaranteed by epoch sync currently), and requires BlockHeight to exist for the height (to check for canonical-ness).

In a case I saw, the former exists somehow (even though it was before the epoch sync boundary) but the latter does not. Not sure why that is the case - I'm confused why the header existed in storage at all.

Either way, this needs to be properly addressed.

@bowenwang1996 Any ideas?